| 摘要 |
1455039 Transistor switching circuits; time control of receivers SABA SCHWARZWAELDER APPARATE-BAU-ANSTALT AUGUST SCHWER SOEHNE GmbH 17 April 1974 [18 May 1973] 16753/74 Headings H3T and H3Q In a circuit for switching off electronic equipment such as a radio 1 after a predetermined time by an electronic timer started by a keying switch 4 the timer comprises a first amplifier 13 having an integrating network including a capacitor 25 and a second amplifier 14 having its inverting input connected to the output of the first amplifier 13 and its output connected via a resistor 29 in a feedback path to its noninvesting input and the output of the second amplifier 14 is connected to the base of a first transistor 33 whose collector is connectible to the base of a second transistor 27 which has its collectoremitter path connected in parallel with the main on-off switch 2 of the electronic equipment 1. As shown the timing period is started by pressing the key switch 4 so as to momentarily engage contacts 7-9, c and d the movable contact of the switch 4 then returning to engage contacts 7-9 b and c. The collector-emitter of the transistor 27 is momentarily bridged by contacts 8c and 8d so as to turn on the radio 1 and a transistor 11 which connects the battery 3 to a stabilizing circuit 12 which stabilizes the supply voltage for the timing circuit at half the battery voltage UB. The momentary contact of contacts 7c and 7d causes a potential lower than a reference potential applied to the inverting input of an operational amplifier 13 to be applied to the non inverting input of the amplifier 13. The subsequent engagement of the contacts 9c and b cause transistor 27 to turn on so as to maintain the radio 1 and the transistor 11 on. After the predetermined time the output voltage determined by 25 and 24 from the amplifier 13 reaches a predetermined value and the output from the amplifier 14 changes positive. This causes transistor 33 to turn on to switch off the transistor 27 and the radio 1 and so end the timing period. During the timing period which can be an hour an ammeter 28 indicates the time still remaining until switch off. If the slider of the potentiometer 24 is set to its upper stop the meter 28 reads half the battery voltage when the timing circuit is switched on so that the meter gives an indication of the on load condition of the battery 3. In the off position 2 of the timing switch 4 the meter 28 is connected as a timing indication with contacts 5a and 6a connected to a discriminator voltage. |
